class_docstr: A Tensorflow(Keras) Conlleval evaluator.
  Runs the conlleval script for given x and y inputs.
  Prints Conlleval F1 score on the end of each epoch.
  
  Args:
      x: features matrix
      y: labels matrix
      y_vocab (dict): int-to-str labels lexicon
      batch_size (:obj:`int`, optional): batch size
code: def on_epoch_end(self, epoch, logs=None):
      predictions = self.model.predict(self.x, batch_size=self.bsz)
      stats = get_conll_scores(predictions, self.y, self.y_vocab)
      print()
      print("Conll eval: \n{}".format(stats))
  
file_path: nlp-architect/nlp_architect/nn/tensorflow/python/keras/callbacks.py
imports: from __future__ import division
  from __future__ import print_function
  from __future__ import unicode_literals
  from __future__ import absolute_import
  import tensorflow
  from nlp_architect.utils.metrics import get_conll_scores
label_desc: Use image node_id 2 for calling the ConllCallback obj's underlying member method code with example usage: obj.on_epoch_end(epoch, logs) without return types